1. Field of the Invention
The present invention relates to a control mechanism having an actuator which employs a shape memory alloy, and relates to a method for adjusting its servo control of the control mechanism.
2. Description of the Related Arts
In recent years, there has been a growing demand and necessity of a miniature mechanism for controlling a position of a driven member to be moved, which can be employed for a compensation mechanism to correct any blurred image caused by a camera shake of a lens shutter camera, for example. In order to satisfy such a demand and necessity, there is proposed an actuator which makes use of a shape memory alloy (or SMA) and a spring. As a method for controlling the actuator which makes use of the shape memory alloy, there has been proposed an on/off controlling method only, in which it is employed as a switch. On the other hand, a xe2x80x9cSystem and Control, Vol. 29, No. 5: Kuribayashi, 1985xe2x80x9d discloses mathematical models of control elements employing the shape memory alloy, and it discloses a PID control. However, it does not disclose any concrete technique thereof.
Accordingly, it is an object of the present invention to provide a control mechanism for controlling position of a driven member by employing an actuator which makes use of the shape memory alloy.
It is another object of the present invention to provide the control mechanism having the actuator which is simple in construction and compact in size.
It is still another object of the present invention to provide a method for adjusting servo control of the control mechanism, in which a driving condition of the control mechanism is stabilized, and in which error in the servo control is small (i.e. accuracy in the servo control is high).
In accomplishing these and other objects of the present invention, according to one aspect thereof, there is provided a control mechanism comprising: a shape memory alloy which memorizes a predetermined dimension thereof; a biasing device for exerting a biasing force on the shape memory alloy and for changing dimension of the shape memory alloy, wherein the shape memory alloy and the biasing device constitute an actuator for moving a driven member which is driven by the actuator, and wherein the driven member is controlled to move in a first direction in which the shape memory alloy returns to the predetermined dimension and in a second direction in which the biasing means changes the dimension of the shape memory alloy, so as to control a position of the driven member, by the actuator; an operation means for performing an operation repeatedly on a basis of information upon a target position and an actual position (or then position or existing position) of the driven member, and for calculating a voltage to be supplied to the shape memory alloy; and a voltage supplier having a limiting circuit for supplying the voltage, calculated by the operation means, to the shape memory alloy, only when the driven member is moved in the first direction, on a basis of a result of the operation performed by the operation means.
In the mechanism, preferably, the biasing device is a spring such as a bias spring.
In the mechanism, the first direction and the second direction may be opposite to each other.
According to the mechanism, the limiting circuit of the voltage supplier limits, or stops, the supply of the voltage, gained by the operation (or calculation) of the operation means, to the shape memory alloy, when the driven member should be moved in the second direction, on a basis of a result of the operation performed by the operation means. By the way, the operation performed by the operation means includes not only the operation (or calculation) of the voltage to be supplied to the shape memory alloy, but also the operation (or calculation) of the voltage corresponding to an electric current to be supplied to the shape memory alloy.
In the mechanism, only when the driven member should be moved in the first direction, the voltage is supplied to the shape memory alloy. As a result, the driven member is moved toward the target position. On the other hand, when the driven member should be moved in the second direction, if the result of the operation performed by the operation means becomes negative, the supply of the voltage to the shape memory alloy is prevented by the limiting circuit of the voltage supplier and thus the driven member is not further driven, nor moved. Namely, with this function, a wrong control is surely prevented, and the driven member is moved towards the target position by the biasing force exerted by the biasing device.
Therefore, according to the arrangement, the control mechanism for controlling the position of the driven member by employing the actuator which makes use of the shape memory alloy is provided
Also, according to the arrangement, because the actuator is constituted by the shape memory alloy and the biasing means such as the spring, the actuator itself becomes simple in construction and compact in size. Therefore, the control mechanism having the actuator also becomes simple in construction and compact in size.
In the mechanism, it is preferable that the limiting circuit of the voltage supplier puts a limit with respect to a final output of the operation means.
According to another aspect of the present invention, there is provided a control mechanism comprising: a shape memory alloy which memorizes a predetermined dimension thereof; a biasing device for exerting a biasing force on the shape memory alloy and for changing dimension of the shape memory alloy, wherein the shape memory alloy and the biasing device constitute an actuator for moving a driven member which is driven by the actuator, and wherein the driven member is controlled to move in a first direction in which the shape memory alloy returns to the predetermined dimension and in a second direction in which the biasing means changes the dimension of the shape memory alloy, so as to control a position of the driven member, by the actuator; an operation means for performing an operation repeatedly on a basis of information upon a target position and an actual position of the driven member, and for calculating a voltage to be supplied to the shape memory alloy; and a voltage supplier having a limiting circuit for limiting a supply of the voltage, calculated by the operation means, to the shape memory alloy, when the driven member is moved in the second direction, on a basis of a result of the operation performed by the operation means.
According to still another aspect of the present invention, there is provided a control mechanism for controlling a position of a driven member in a first direction and in a second direction by an actuator, the control mechanism comprising: a target position determination means for determining a target position to which the driven member is to be moved; an actual position detection means for detecting an actual position of the driven member; and a control output operation means for calculating a control output with a phase being led (or with a phase being forwarded or with a phase being fast) by executing an operation which includes a differential calculus executed twice relative to a difference between the target position and the actual position.
By executing the operation including the differential calculus executed twice, or more than twice, relative to the difference between the target position and the actual position, it is possible to compensate a phase by 180xc2x0 or more. As a result, a control with higher response is realized.
In the above mechanism, the actuator can be constituted by: a shape memory alloy which memorizes a predetermined dimension thereof; and a biasing device for exerting a biasing force on the shape memory alloy and for changing dimension of the shape memory alloy.
In the mechanism, preferably, the biasing device is a spring.
Alternatively, the actuator can be constituted by a pair of shape memory alloys one ends of which are connected to each other.
By the way, an output value (value of voltage, for example) calculated by the control output operation means is outputted to an driver for the actuator, on the basis of which the actuator is driven by the driver.
As an embodiment of the control output operation means for executing the operation which includes the differential calculus executed twice, the control output operation means can execute a PDD control.
The PDD control is a control by proportion (or proportional operation), differential calculus and differential calculus. Physically, the PDD control is of a control operation (or control calculation) carried out in view of the positional difference between the target position and the actual position, the difference in speed (or velocity), and the difference in acceleration.
Although the driven member is not particularly limited, the driven member, for example, can be an optical system for compensating a shake, caused by a manual operation, of an optical apparatus in which the control mechanism is provided.
According to still another aspect of the present invention, there is provided a control mechanism for controlling a position of a driven member in a first direction and in a second direction by an actuator, the control mechanism comprising: a target value determination means for determining a target value with which the driven member is to be moved; an actual value detection means for detecting an actual value of the driven member; and a control output operation means for calculating an optimal control output by executing leading compensations more than once relative to a difference between the target value and the actual value.
In the mechanism, the position of the driven member is controlled on the basis of the positional difference between the target position and the actual position, the difference in speed (or velocity), the difference in acceleration.
According to still another aspect of the present invention, there is provided a control mechanism comprising: a shape memory alloy which memorizes a predetermined dimension thereof; a biasing device for exerting a biasing force on the shape memory alloy and for changing dimension of the shape memory alloy, wherein the shape memory alloy and the biasing device constitute an actuator for moving a driven member which is driven by the actuator, and wherein the driven member is controlled to move in a first direction in which the shape memory alloy returns to the predetermined dimension and in a second direction in which the biasing means changes the dimension of the shape memory alloy, so as to control a position of the driven member, by the actuator; a target position determination means for determining a target position to which the driven member is to be moved; an actual position detection means for detecting an actual position of the driven member; a control output operation means for calculating a control output by executing an operation relative to a difference between the target position and the actual position; and a compensation means for restraining heating of the shape memory alloy with respect to a result of the operation executed by the control output operation means in order to stabilize a drive control of the actuator.
In the mechanism, a spring such as a bias spring can be employed.
According to the mechanism, the shape memory alloy is prevented from rather overheating by the compensation means, so that the driving characteristic (or driving property) of the actuator is stabilized.
By the way, the output value (value of voltage, for example) which is calculated by the control output operation means and which is compensated (or corrected) by the compensation means, is outputted to the driver for the actuator, on the basis of which the driver actually drives the actuator.
According to still another aspect of the present invention, there is provided a control mechanism comprising: a shape memory alloy which memorizes a predetermined dimension thereof; a biasing device for exerting a biasing force on the shape memory alloy and for changing dimension of the shape memory alloy, wherein the shape memory alloy and the biasing device constitute an actuator for moving a driven member which is driven by the actuator, and wherein the driven member is controlled to move in a first direction in which the shape memory alloy returns to the predetermined dimension and in a second direction in which the biasing means changes the dimension of the shape memory alloy, so as to control a position of the driven member, by the actuator; a target position determination means for determining a target position to which the driven member is to be moved; an actual position detection means for detecting an actual position of the driven member; a control output operation means for calculating a control output by executing an operation relative to a difference between the target position and the actual position; and a compensation means for correcting a voltage which is supplied to the shape memory alloy with respect to a result of the operation executed by the control output operation means, in which the correction of the voltage is made by adding an offset voltage.
In the mechanism, the value of the offset voltage is determined by, for example, giving a quasi shake (or false shake or pseudo shake) to the control mechanism before the control mechanism is shipped as a commercial product.
In the mechanism, it is preferable that the value of the offset voltage is negative.
According to still another aspect of the present invention, there is provided a method for adjusting servo control of a control mechanism, in which the control mechanism comprises: a shape memory alloy which memorizes a predetermined dimension thereof; a biasing device for exerting a biasing force on the shape memory alloy and for changing dimension of the shape memory alloy, wherein the shape memory alloy and the biasing device constitute an actuator for moving a driven member which is driven by the actuator, and wherein the driven member is controlled to move in a first direction in which the shape memory alloy returns to the predetermined dimension and in a second direction in which the biasing means changes the dimension fag of the shape memory alloy, so as to control a position of the driven member, by the actuator; a target position determination means for determining a target position to which the driven member is to be moved; an actual position detection means for detecting an actual position of the driven member; and a servo control circuit which executes a servo control on the basis of information upon the target position and the actual position, the method comprising the steps of: optimizing a gain setting of the servo control circuit within a predetermined permissible range; detecting the actual position to which the driven member is actually driven to move, after the optimization, by the actual position detection means, and actually measuring a difference between the actual position and the target position; and making the control mechanism itself memorize the difference thus measured actually.
In the method, it is preferable that the biasing device is a spring such as a bias spring.
According to the servo control adjustment method, the difference between the actual position and the target position is actually measured, and the control mechanism itself is made to memorize the difference thus measured actually. That is, according to the method, a servo control on the basis of the difference such as an offset error etc., memorized, or stored, on the control mechanism itself, is carried out. Therefore, with the method, not only the driving condition of the control mechanism is stabilized, but also the error in the servo control becomes small (i.e. the accuracy in the servo control becomes high).
Preferably, the servo control circuit comprises a compensation circuit for restricting heating of the shape memory alloy so that a drive control of the actuator is stabilized, and the step of optimizing the gain setting thereof further comprises a step of optimizing a value of compensation which is executed by the compensation circuit.